JP4632665B2 - Simultaneous metering of organic initiator and protective colloid during the polymerization reaction - Google Patents

Abstract

The invention pertains to a process wherein initiators and protective colloids are both metered to a polymerization mixture. This manner of metering allows for improved control of the polymerization rate and an improved reactor space-time yield, and the process will render a polymer with a relatively high porosity.

Description

The present invention relates to a process for polymerizing one or more monomers wherein one or more organic initiators are metered into the polymerization mixture at the reaction temperature.

Such a process is known from German Offenlegungsschrift 1 570 963, where the initiator was metered into the polymerization reactor. The initiator employed is an organic peroxide such as peroxydicarbonate. Peroxydicarbonate usually has a relatively long half-life in the range of 3.5 to 4.5 hours at a polymerization temperature of 54 ° C.

Compared with the method of German Offenlegungsschrift 1 570 963, the polymerization rate is improved when using the method disclosed in WO 00/17245. Here, the organic peroxide is metered into the polymerization reactor at a temperature at which the peroxide has a half-life of 0.05 to 1.0 hour. By selecting the appropriate peroxide and the appropriate metering conditions, the heat of polymerization can be controlled to a certain level, resulting in a high polymer yield, the use of a very efficient peroxide, and in the resin after polymerization. Can result in low residual peroxide levels.

Unpublished US Patent Application No. 60 / 342,434 discloses a method that allows for shorter polymerization times than International Patent Application Publication No. 00/17245. Here, it is taught to meter organic peroxide into the polymerization reactor at a temperature at which the peroxide has a half-life of 0.0001 to 0.05 hours. This process allows for better thermal control during polymerization, improved reactor space time yield, and even lower residual peroxide concentration in the resin.

However, it has been found that in these reactions, the efficiency of the initiator is usually insufficient, resulting in a relatively high dosage concentration of initiator and a high concentration of undesirable degradation products. Depending on the nature of the degradation product, the odor and / or color of the resin may not be acceptable. It is also known that residual degradation products that typically have a molecular weight of less than 250 daltons can result in haze that is undesirable (the degradation products evaporate from the resin and condense on other surfaces).

EP 718314 discloses a two-stage process for polymerizing acrylic and methacrylic monomers. Here, in the first stage, a large amount of protective colloid in the range of 4 to 15% by weight is mixed and heated, after which the solution is cooled and the monomer mixture is added. In the second stage, the resulting mixture is again heated in the presence of an organic initiator. The large amount of protective colloid that is required provides a very complex method with long reactor times (about 7 hours) to make (meth) acrylic polymers.

It is an object of the present invention to provide an improved and simple method using a small amount of protective colloid and a short reaction time. This overcomes the drawbacks of the prior art methods while at the same time yielding a resin with the desired properties for PVC resin, such as porosity.

The method of the present invention is such that at least a portion of the total amount of one or more organic initiators is metered into the polymerization mixture at the reaction temperature and at least a portion of the total amount of one or more protective colloids is metered in. That's the way.

By metering both initiator and protective colloid, the efficiency of the initiator is improved, increasing the polymerization rate and reducing the polymerization time compared to the above technique. Furthermore, the pressure drop rate has been found to increase, which further improves the reactor space time yield that can be obtained. In addition, the porosity of the polymer can be increased and well controlled by the selection of suitable protective colloids and the way in which protective colloids and / or peroxides are metered in. A further advantage is that the fisheye content is reduced.

A process is known from US Pat. No. 5,376,747 in which the peroxide is all added to the reaction mixture at the start of the polymerization reaction and the protective colloid is metered into the mixture. This method aims to produce polymers based on vinyl chloride having an effectively reduced number of fish eyes without losing thermal stability. It does not teach the metering of peroxide to achieve a higher polymerization rate, and it does not disclose the simultaneous metering of protective colloid and peroxide, which further increases the rate. .

Unconstrained theory can explain the working principle of the present invention. The polymerization rate depends on the initiator initiation rate (k _init ), which is proportional to the efficiency factor (f) and the degradation rate (k _d ). The degradation rate is inversely proportional to the half-life of the initiator, which is proportional to the temperature dependent activity factor (e ^{−Ea / RT} ). It will be apparent to those skilled in the art that by metering in a rapid initiator with a shorter half-life, the polymerization rate can be increased due to the higher degradation rate k _d . It is believed that metering protective colloids, among other things, affects the efficiency factor f for these rapid initiators. Therefore, metering both initiator and protective colloid has a synergistic effect on the polymerization rate and to a greater extent compared to just changing the disclosed agent or just changing the protective colloid. To increase.

The process according to the invention is particularly suitable for polymerizing monomer mixtures containing vinyl chloride monomer (VCM). Preferably, the process according to the invention comprises the polymerization of a monomer mixture comprising at least 50% by weight (% w / w) VCM, based on the weight of all monomers. Comonomers that can be used are those of conventional type and include vinylidene chloride, vinyl acetate, ethylene, propylene, acrylonitrile, styrene, and (meth) acrylates. More preferably, at least 80% by weight of the monomer to be polymerized is supplied by VCM, while in the most preferred method, the monomer consists essentially of VCM. As known to those skilled in the art, to a large extent, the polymerization temperature of such a process determines the molecular weight of the resulting resin.

One or more protective colloids can be used in the method of the present invention. Examples of suitable protective colloids have a degree of hydrolysis of at least 40%, more preferably at least 60%, and most preferably at least 62%, and up to 90%, more preferably up to 85%, and most preferably up to Protective colloids such as polyvinyl alcohol (PVA), which can be (partially) saponified polyvinyl acetate with a degree of hydrolysis of 80%. For example, if two PVAs are used, both PVAs may have similar degrees of hydrolysis. It can also be considered that the two PVAs have different degrees of hydrolysis. The first PVA can have a degree of hydrolysis as described above. The second PVA may have a degree of hydrolysis of at least 10%, more preferably at least 20%, and most preferably at least 30%, and up to 80%, more preferably up to 70%, and most preferably up to It can have a degree of hydrolysis of 60%. If more than one PVA is used, the degree of hydrolysis shown is usually the weight average degree of hydrolysis of the product used. Although the PVA is the preferred protective colloid for the process according to the invention, other conventional protective colloids such as cellulosic water-soluble polymers, oil-soluble emulsifiers or water-soluble emulsifiers can also be used. Examples of such cellulose are methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose. Examples of water soluble polymers are polyacrylic acid, gelatin, styrene maleic acid copolymer, and polyvinyl pyrrolidone. Oil-soluble emulsifiers are, for example, sorbitan monolaurate, sorbitan trioleate, sorbitan monostearate, glycerin tristearate, and ethylene oxide-propylene oxide block copolymers. Examples of water-soluble emulsifiers are polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerine oleate, and sodium laurate. Copolymers using combinations of two or more of the above protective colloids are also contemplated.

The protective colloid can be in pure form or diluted in a suitable solvent. Here, in the case of PVA, it is preferably water or a mixture of water and alcohol. The aqueous solution may contain at least 0.5 wt% PVA, more preferably at least 1 wt% PVA, and most preferably at least 2 wt% PVA, and up to 10 wt% PVA, more preferably up to 5 wt%. PVA, and most preferably up to 4% by weight PVA may be included.

The amount of protective colloid used in the process according to the invention is in a lesser range, as is conventionally used in polymerization processes. Typically this range is based on the weight of the monomer to be polymerized and is a lower limit of 0.01% and more preferably 0.02% by weight of protective colloid, and 1%, preferably 0.3% and most preferably. It has an upper limit of 0.15% by weight protective colloid.

In the process according to the invention, one or more initiators are used. These initiators can be any type of organic peroxide suitable for use in the polymerization process, such as peroxydicarbonate and acetyl-cyclohexyl-sulfonyl-peroxide. More preferred initiators are rapid initiators, for example organic peroxides having a half-life of 0.0001 to 1 hour. More preferred is a peroxide having a half-life of 0.0001 to 0.5 hours.

Preferred examples of the organic peroxide used in the method of the present invention include 1,1,3,3-tetramethylbutyl peroxymethoxyacetate, tertiary-butylperoxymethoxyacetate, tertiary-amylperoxymethoxyacetate, Tertiary-butylperoxyethoxy acetate, diisobutanoyl peroxide (TrigonoxTM 187), hexanoyl pivaloyl peroxide, 2-ethyl-butanoyl-isononanoyl peroxide, isobutanoyl-lauroyl peroxide, isobutanoyl-isononano Yl peroxide, bis (tertiary-butylperoxy) oxalate, cyclododecyl-tertiary-butylperoxyoxalate, 2,2-bis-2-ethylhexanoylperoxy-4-methylpentane, 2,2- Bis-2- Tylbutanoylperoxy-4-methylpentane, 2,2-bis (2,2-dimethylpropanoylperoxy) -4-methylpentane, 1- (2-ethylhexanoylperoxy) -1,3-dimethyl Butyl-1-peroxypivalate (Trigonox® 267) or 2,4,4-trimethylpentyl-2-peroxyneodecanoate (Trigonox® 423), tertiary-amyl peroxyneodecano Ate (TrigonoxTM 123), tertiary-butyl peroxyneodecanoate (TrigonoxTM 23), benzene (m, p) di (2-isopropyl-2-peroxyneodecanoate), 2 -Methyl-4-hydroxypentane-2-peroxyneodecanoate, α-cumylperoxyneodecanoate (Trigonox® 99), and peroxydicarbonates such as di-secondary-butylperoxy- Dicarbonate (Tr igonox ™ SBP), di (4-tertiary-butylcyclohexyl) peroxydicarbonate (Perkadox ™ 16) and di (2-ethylhexyl) peroxydicarbonate (Trigonox ™ EHP).

Other organic peroxides having a half-life in the range of 0.0001 to 1 hour at the polymerization temperature can also be used. Whether a peroxide has an appropriate and desired half-life can be determined by conventional pyrolysis studies in monochlorobenzene, well known to those skilled in the art (e.g., code 10013921001 booklet “Initiators for high polymers, which can be obtained from Akzo Nobel). ).

In the process of the present invention, it is not very effective to use a rapid initiator during the polymerization stage of the so-called cold start process, in which the reactor contents are heated to the desired polymerization temperature. However, if desired, one or more rapid and / or more conventional initiators can be used at this stage. If a conventional initiator is used, this initiator preferably has a conversion, or degree of polymerization, of less than 80%, preferably less than 50%, more preferably of all monomers used in the process. When less than 30%, more preferably less than 10%, and most preferably less than 2%, it will be introduced into the reaction mixture before the heating stage or immediately after the heating stage.

If the reaction mixture is administered at or near the polymerization temperature, the so-called warm start method does not require a certain amount of initiator to be added at the start, while the remainder is metered in over time. However, also in this warm start method, immediately after the formation of the reaction mixture, a maximum of 60 wt. It may be advantageous to add%, more preferably up to 4% by weight, even more preferably up to 2% by weight, and most preferably up to 1% by weight, the rest being metered in over time. This approach is particularly preferred if a certain amount of polymerization inhibitor (radical scavenging species) is present in the reaction mixture. For example, if such a radical scavenger is typically used as a stabilizer where it is introduced with the monomer so that it is present, the initially metered initiator will be combined with the stabilizer. Reacts and thus prevents delayed initiation of the polymerization reaction.

The amount of initiator (or initiators) to be used in the process of the present invention is within the range conventionally used in polymerization processes. Typically this range is based on the weight of the monomer to be polymerized, 0.01% by weight, more preferably 0.02% by weight lower limit of initiator, and 1% by weight, preferably 0.3% by weight, most preferably 0.2%. Has an upper limit of wt% initiator.

The initiator is metered into the reactor in pure form or preferably in the form of a diluted solution or dispersion (eg, a suspension or emulsion). One or more suitable solvents can be used to dilute the initiator. Preferably, such solvents are easily removed during the stage where the polymer is processed after the polymerization process, such as alcohols, or they are the desired plasticizer for the final resin. As in the case of solvents, it is of a nature such that it is permissible to remove them as residues in the final polymer. Furthermore, such solvents may not negatively affect the thermal stability of the initiator dissolved therein, as can be demonstrated by analyzing the half-life temperature of the initiator in the solvent. May be advantageous, but not necessarily required. An example of such a solvent is isododecane. If an initiator dispersion is metered in, then the dispersion can be either the initiator itself or preferably a solution of the initiator in the appropriate solvent. Preferably, the dispersion is an aqueous dispersion. Preferably, the initiator is at least 0.1 wt%, more preferably at least 0.5 wt%, and most preferably at least 2 wt%, and up to 75 wt%, more preferably up to 60 wt%, and even more preferably up to 50 wt%. %, Even more preferably up to 25% by weight and most preferably up to 15% by weight. A more diluted initiator solution or dispersion ensures rapid mixing of the initiator and the polymerization mixture, which is more efficient for the initiator that is important for the rapid initiator used. Bring use.

During the polymerization reaction, rapid initiators and protective colloids can be added simultaneously or separately, either in alternating mode or in a continuous random order at the polymerization temperature. A portion of the protective colloid can be added to the reaction mixture prior to the addition of the initiator during either the cold start or warm start process. This is to ensure that the monomer to be polymerized is properly dispersed in the reaction mixture. This portion may be at least 1%, preferably at least 5%, and most preferably at least 10%, and at most 50%, preferably at most 30%, and most preferably at most 20% of the total protective colloid. The remaining portion is then added as follows.

The initiator and protective colloid moiety are either alternating or continuous in a random order in the reactor with at least 2 moments, preferably at least 4 moments, more preferably at least 10 moments, and most preferably at least 20 moments. Can be added separately. The amount of initiator can be the same or can vary with each part or number of initiator parts. Each subsequent (numbered) initiator portion can be varied to include more (or less) initiator if desired. The amount of protective colloid can be the same in each colloid part, in a manner similar to the initiator part, or can be varied individually or in groups.

Rapid metering of the initiator and protective colloid can also proceed simultaneously, which means that at least 20%, preferably at least 40%, more preferably at least 60% of all monomers used in the process are polymerized. Can be done intermittently or continuously over a period of time. If intermittent operation is chosen, at least 2 moments, preferably at least 4 moments, more preferably at least 10 moments, and most preferably at least 20 moments at the polymerization temperature at which the initiator and protective colloid are metered in. is there. If desired, intermittent and continuous operations are combined, so the initiator and / or protective colloid is intermittently metered in for a period (longer or shorter). Most preferably, the initiator and protective colloid are at least 1%, preferably at least 5%, more preferably at least 10%, more preferably at least 20%, and even more preferably at least 30% of the monomer has already been polymerized. Continuously and / or intermittently metered, where at least 10%, preferably at least 20%, more preferably at least 30%, and most preferably at least 50% of all monomers used in the process Is polymerized during metering.

The amount of initiator and protective colloid can be the same or can be varied with each part or number (and each other) of the intermittently metered parts. These can be varied so that each subsequent initiator moiety contains more (or less) initiator if desired. When the initiator and protective colloid are metered continuously, these amounts can be constant, or they can gradually increase (or decrease) during the metering operation, and in this case, The amount of initiator and protective colloid can vary from one another, in which one of the two components can be held in a constant amount. Optionally, although less desirable, the administered initiator and / or protective colloid is combined with water and / or monomers to prevent, for example, volume reduction of the polymerization mixture or to the monomers to be polymerized. Facilitates initiator transport.

Preferably metering of initiator and PVA can be accomplished at any suitable entry point to the reactor. Such entry points can be located below or above the surface of the reaction mixture, if desired. The initiator and protective colloid can be added separately to the reactor via two respective inlet points, or they can be premixed and enter the reactor through one inlet. If water is added during the polymerization process, for example to compensate for the reduction in reactor contents for the polymerization reaction, and this water is added to meter the initiator and / or protective colloid. It may be advantageous to use piping that is metered in. In order to ensure better, faster and more uniform mixing of initiators and / or protective colloids in the reactor mixture, the reactor includes a plurality of inlet points located at different locations around the reactor It can also be considered. If the reactor further comprises a reflux condenser, it is contemplated to add protective colloid to the reaction mixture via the reflux condenser through one or more inlet points.

The polymerization process may be as a bulk process where the reaction mixture is primarily monomeric, or more preferably as a suspension process where the reaction mixture is typically a (micro) suspension of monomer in water, or the monomer Can be carried out as an emulsification or microemulsification process, typically emulsified in water. In these processes, the usual additives will have to be used. For example, if the monomer is present in the form of a suspension in water, conventional additives such as surfactants, antifoams, pH buffers and the like may be present. Depending on the type of polymer desired, any of the above processes may be preferred. Due to the small amount of protective colloid required, the process according to the invention is particularly suitable for use in microsuspension or suspension processes. Most preferably it is a suspension polymerization process.

The bulk and preferred suspension processes can be carried out in batch or continuous reactors. In a batch process, monomer polymerization proceeds and terminates in one reactor. The resulting polymer is then removed from the reactor and isolated. The polymerization process can also be carried out in a continuous reactor with a certain time before entering the reactor and leaving the reactor, ie the residence time, the amount of monomer remaining in the reactor. The residence time is at least 1%, preferably at least 5%, and most preferably at least 10%, and at most 99%, preferably at most 96%, more preferably at most 90% of the amount of monomer entering the reactor, and Most preferably up to 85% is chosen long enough to be polymerized before leaving the reactor. The resulting polymer is at least partially removed from the reactor or from the flowing fluid and subsequently separated. After removal of the polymer, a new portion of monomer is added to the reactor to at least partially compensate for the polymerized amount of monomer removed. In this way, the space-time yield is further improved compared to batch processes.

The process according to the invention makes it possible to achieve the polymerization reaction within 4 hours, preferably within 3 hours, more preferably within 2 hours and most preferably within 1 hour. The polymerization time can be defined as the time during which the monomer is still polymerized at a significant polymerization rate. When a constant pressure in the reactor is observed and then a pressure drop occurs, the polymerization time includes at least this constant pressure time. In a continuous process, the pressure does not drop or simply drops slightly, so that the reactor can always have a constant pressure. In such an event, the percentage of polymer formed in relation to the monomer added globally per hour (% by weight) or the monomer converted per hour relative to the monomer added globally per hour Percentage (wt%) gives a good indication of the polymerization rate. The polymerization time depends on the amount and type of initiator used, the amount and type of protective colloid, the method in which the protective colloid and initiator are metered in, the reaction temperature and the like. By choosing the correct parameters, the time can be minimized, thus further improving the reactor space time yield.

After polymerization, the resulting (co) polymer (or resin) will be processed as usual for those skilled in the art. The polymer obtained by suspension polymerization according to the invention will for example be subjected to the usual drying and screening steps. The resulting resin is preferably dried at 60 ° C. for 1 hour and immediately after screening, it contains less than 50 ppm, more preferably less than 40 ppm, and most preferably less than 25 ppm residual initiator. Features. The resin was found to exhibit excellent thermal stability as measured by a Metrastat ™ PSD260 test furnace according to ISO 182-2 (1990E). The improved thermal stability proved that the resin hardly discolored when subjected to a melt processing stage, for example, to form a molded article.

A non-limiting example is given below to demonstrate the unexpected effect of simultaneous metering of PVA in the continuous metering of peroxide during PVC suspension polymerization. The example was not optimized.

Examples In a standard suspension polymerization experiment, a temperature controlled 1 liter of 1 liter equipped with one baffle, three blade stirrer, pressure transducer, vinyl chloride (VCM) supply line, and nitrogen purge line. Stainless steel Buchi reactor is 425 grams of deionized water, Alcotex ™ B72 (polyvinyl acetate / alcohol) in 5% solution in deionized water, quantities and metering as shown in Tables 1 and 2 Filled with feeding procedure (warm start and continuous peroxide metering) and pressurized to 15 bar G with nitrogen. If leaks are observed, the reactor is degassed and pressurized with nitrogen to 5 bar G three times to expel substantially all of the air. The reactor was then degassed and charged with 250 grams of Akzo Nobel Salt & Basics VCM, and then the reactor was heated to the polymerization temperature for 30-60 minutes. Initiator and protective colloid amounts and metering procedures are also shown in Tables 1 and 2. After either a pressure drop of 2-3 bar in the reactor or the first visit of 4.5 hours of reaction time, the polymerization is continued for another 30 minutes without metering initiator and / or protective colloid. And then the reactor was cooled to 20-25 ° C., degassed, and virtually all remaining VCM was removed. The polymer was obtained after filtration, washing and drying (1 hour at 60 ° C. using a fluid bed). The time to pressure drop in the reactor is the constant pressure time (CPT). Using the above experimental setup, the 5 minute difference in CPT is considered to be dominant.

The heat formed during the polymerization process was measured and the cooling was adapted to the heat formed. The more heat is generated at a certain time, the more difficult it will be to control the temperature of the reaction mixture. A low exothermic peak with high polymer yield is preferred because optimization in reactor space time yield can then be achieved.

Example Two initiators were used: Trigonox ™ 187 and Trigonox ™ 267. The metering procedures and polymerization results for each individual initiator are shown in Tables 1 and 2.

After reaching the polymerization temperature, the parts shown in the Trigonox® 187 (or Trigonox® 267) table per million parts of VCM (measured as 0.8 wt% methanol solution) are shown. Over time. After the first metering, the metering rate was reduced to a lesser extent (see quantity and time shown in the table). When co-feeding PVA, a solution of Trigonox ™ 187 (or Trigonox ™ 267) and a solution of PVA in water were mixed and continuously stirred.

Examples 1 and 2 show faster polymerization rates where simultaneous metering of peroxide and PVA results in clearly shorter CPT, resulting in shorter polymerization times and faster pressure drops. Virtually less peroxide can be used to obtain a similar reactor space time yield (PVC yield) when the peroxide and PVA are co-metered. Table 2 further shows that simultaneous metering results in a clearly improved porosity of the resulting polymer.

Claims (18)

In a method of polymerizing a polymerization mixture comprising at least one monomer, at least one monomer is vinyl chloride, at least an organic initiator and 0.01 to 1 wt% protective colloid based on the weight of the monomer to be polymerized, Process where the polymerization mixture is metered in at the polymerization temperature. The process according to claim 1, wherein the protective colloid is polyvinyl alcohol or saponified polyvinyl acetate having a degree of hydrolysis of 40-90%. The process according to claim 1 or 2 , wherein the organic initiator has a half-life of 0.0001 to 1 hour at the polymerization temperature. 4. A method according to any one of claims 1 to 3 , wherein the initiator and the protective colloid are at least partly metered simultaneously. The process according to any one of claims 1 to 4 , wherein the metering of the initiator and protective colloid is controlled such that the maximum cooling capacity of the reactor is used. At least a portion of the initiator and at least a portion of the protective colloid are metered intermittently and / or continuously over a period in which at least 20% of all monomers used in the polymerization are polymerized. However, the method according to any one of claims 1 to 5 . After at least 1% of the one or more monomers have already been polymerized, at least a portion of the initiator and protective colloid is metered intermittently and / or continuously and during the metering period, the method according to any one of claims 1-5 at which at least 10% of all monomers used are polymerized in the process. The residence time of the polymerization time or continuous process of a batch process is shorter than 4 hours, and in any one of claims 1 to 7 where a sufficient length to at least 1% of the amount of monomer is polymerized The method described. Claims having less than 50 parts by weight of remaining initiator as measured immediately after polymerizing and drying the (co) polymer for 1 hour at 60 ° C, based on 1 million parts by weight of the (co) polymer. A (co) polymer based on vinyl chloride obtainable by the process according to any one of 1-8 . 10. A method of using a vinyl chloride (co) polymer according to claim 9 in a molding method comprising heating the (co) polymer above the melting temperature of the (co) polymer. 4. The method according to claim 3 , wherein the half-life is 0.0001 to 0.5 hours. The method of claim 7 , wherein the initiator and protective colloid are metered after at least 5% of the monomer has already been polymerized. 8. The method of claim 7 , wherein the initiator and protective colloid are metered after at least 10% of the monomer has already been polymerized. 8. The method of claim 7 , wherein the initiator and protective colloid are metered after at least 20% of the monomer has already been polymerized. 8. The method of claim 7 , wherein the initiator and protective colloid are metered after at least 30% of the monomer has already been polymerized. At least 20% of all monomer is polymerized, the method according to any one of claims 7 and 1 1 to 1 5. The process of any one of claims 7 and 11 to 15 wherein at least 30% of all monomers are polymerized. 16. A process according to any one of claims 7 and 11 to 15 wherein at least 50% of all monomers are polymerized.